1. Field of the Invention
The present invention relates, in general, to a handling device and a method for handling elongate molded articles, and is particularly, but not exclusively, applicable in a system for handling large injection molded preforms, e.g. elongate preforms that are subsequently blow-molded into 10 to 25-liter water bottles.
2. State of the Art
To date, there has been a tendency for large beverage containers and the like, e.g. the aforesaid 10 to 25-liter water bottles, to be manufactured in polycarbonate in an extrusion manufacturing process. Polycarbonate is however relatively soft and therefore susceptible to surface damage, e.g. scratching, and its manufacturing process is generally costly.
Recently there has been a general movement and desire to produce such large containers in polyethylene tetraphthalate (PET), especially since the processing of PET can be performed in an injection molding environment and, besides increased ease of recycling of the molded article and increased resilience to scratching, the optical quality of PET injection molded articles is generally better than corresponding polycarbonate articles. Furthermore, the injection molding process also yields molded articles having repeatably attainable, highly-toleranced physical dimensions which therefore ensures enhanced part quality. In the manufacture of injection molded articles, e.g. in the context of preforms for food and beverage applications and the like, an injection molding machine can support a mold with multiple mold cavities so that a number of articles can be molded in a single molding cycle. For large or heavyweight preforms, generally considered to weigh in excess of about 100 g, and typically more, a mold configuration may be laid out as two columns of eight preforms. Large or heavyweight preforms often have lengths dimensions generally in excess of about 20 cm, and diameters of about 5 cm. For smaller preforms, mold cavitation sizes are considerably smaller and accordingly the number of mold cavitations can be considerably larger, with manufacturers presently offering systems with up to 144 cavities. After the plastics melt has been injected into the mold cavities, the mold must remain shut, to allow sufficient solidification of the melt into the article to allow handling of the article without causing meaningful deformation.
The number of preforms formed in an injection molding cycle depends on the number of injection mold cavities, with the number of cavities also dependent upon the plastic volume throughput per cycle of the extruder and injection unit. For very heavyweight preforms, e.g. preforms for 10 to 25-liter bottles, injection molding machines typically support cavitations of between about 1 to 8 cavities, although other cavitations are possible, subject to machine tonnage, extruder throughput and cycle time. The cavities, for optimized cooling purposes, are generally aligned in parallel columns of cavities, with all cavities in adjacent columns also aligned in a horizontal plane to form a symmetrical rectangular array. Of course, adjacent parallel columns could have their respective cavities offset or staggered.
The cycle time of such an injection molding process varies according to the size of the molded article being manufactured, with smaller articles, e.g. preforms suitable for blowing into 500 ml bottles, requiring less time to inject and sufficiently solidify than larger articles, such as preforms designed to be blown into 10 to 25-liter water bottles, which can have preforms weights of about 500 to 700 although larger (heavier) preforms are also being considered. Essentially, the cycle time is related to the mass and thermal dissipation characteristics of the molded article, with thicker preforms having better insulative properties arising from the poor thermal transfer characteristics of plastics, particularly PET and PEN (polyethylene). Once the articles have solidified sufficiently to allow handling, the mold is opened and the articles are ejected from the mold. European patent EP describes the use of intimate fit cooling tubes for removing molded articles, such as preforms, from the mold and delivering them to a conveyor system.
Generally, the articles are dropped from the injection mold or the cooling tubes onto a conveyor, which then transports the articles and drops them into a shipping crate. It has, however, been noted that, when the articles are ejected from the cooling tubes, they are prone to damage and deformation; this is particularly true for larger articles such as preforms for 10 to 25-liter water bottles. Damage, such as surface scratching, can also occur and be accentuated when the articles are loaded into shipping crates or the like. Furthermore, from a logistical movement perspective, it is desirable to load the molded articles into shipping crates in an efficient and compact way to optimize the number of articles in each crate.